People often talk with some drama about the smell of fear, and yet who among us could describe what the odour is like? This vagueness seems to support the idea that fear as a smell is metaphorical – a way raconteurs through the ages have conveyed the tendency for fear to spread rapidly and invisibly from one person to the next. A new study, however, suggests there is, after all, a literal truth to the idea of fear being communicated through our sense of smell.

Alexander Prehn-Kristensen and colleagues bottled the smell of fear by placing cotton pads under the arms of students waiting to give an assessed oral presentation. For comparison the researchers also collected fear-free sweat from the armpits of students performing cycling exercises.

Next the researchers scanned the brains of 28 students while the two sources of odour were delivered to their noses using an adapted oxygen mask. Half the time, the students couldn’t even perceive an odour. They were also unable to distinguish between the two odour sources, rating them as equally pleasant. Crucially, however, the participants’ brain responses to the two odours did differ significantly.

The smell of sweat taken from students anxiously awaiting an oral exam led to proportionately greater activation in the participants across a swathe of brain areas known to be involved in empathy, emotion, representing other people’s mental states and distinguishing the self from other. These included the insula, the precuneus, the cingulate gyrus, the fusiform cortex and the dorsomedial prefrontal cortex.

This finding, of the smell of fear triggering an emotional brain response in the absence of any conscious awareness, could help explain why we’re sometimes moved by a whiff of fear in the air, without registering any accompanying sensory experience. “It is concluded that the human brain automatically guides physiological adjustments to chemosensory anxiety signals, without being dependent on conscious mediation,” the researchers said. _________________________________